[The predictive value of bone mineral density in different parts of the vertebral body for postoperative cage subsidence in anterior cervical discectomy and fusion].

<b>Objective:</b> To explore the effects of bone mineral density (BMD) on postoperative cage subsidence in patients undergoing anterior cervical discectomy and fusion (ACDF) in different regions of the vertebrae. <b>Methods:</b> The study is a retrospective case-control analysis. The clinical and imaging data of 164 cervical spondylosis patients who underwent ACDF at Department of Spine Surgery, the Third Hospital of Hebei Medical University between January 2021 and June 2024 were retrospectively reviewed. Data from 147 patients (230 intervertebral spaces) constituted the analysis set, including 80 males and 67 females, with an age of (54.5±11.2) years (range: 32 to 81 years). Patients were grouped based on postoperative cage subsidence: 74 patients were included in the subsidence group, and 73 patients were included in the non-subsidence group (grouped by patients); 99 intervertebral spaces were included in the subsidence group, and 131 intervertebral spaces were included in the non-subsidence group (grouped by intervertebral space). Cage subsidence was defined as a≥3 mm loss of intervertebral height at the operated level on lateral radiographs during follow-up. Cervical BMD was assessed using Hounsfield Units (HU) values obtained from CT images. Independent sample <i>t</i>-test or Chi-squared test were used to compare baseline characteristics between groups. Multivariate Logistic regression analyzed the influence of HU values at different locations on cage subsidence. Receiver operating characteristic (ROC) curve analysis calculated the area under the curve (AUC) to evaluate the predictive value of HU values for cage subsidence and determine optimal thresholds. The Delong test compared the predictive differences for subsidence among HU values from different vertebral locations at the surgical fixation levels. A validation set comprising clinical data from 17 single-level surgery patients was used to further verify the accuracy of the established thresholds for predicting cage subsidence. <b>Results:</b> In the analysis set, there were no statistically significant differences in age, sex, body mass index, or underlying diseases between patients in the subsidence group and the non-subsidence group (all <i>P</i>>0.05). The HU values of subsided intervertebral spaces were lower than those of non-subsided intervertebral spaces (upper vertebra: 360.1±86.4 <i>vs</i>. 301.7±93.3, <i>t</i>=4.899, <i>P</i><0.01; lower vertebra: 328.8±83.6 <i>vs</i>. 282.5±88.1, <i>t</i>=4.062, <i>P</i><0.01; endplate of the upper vertebra: 604.7±150.9 <i>vs</i>. 521.6±125.3, <i>t</i>=4.446, <i>P</i><0.01; endplate of the lower vertebra: 554.4±157.9 <i>vs</i>. 502.8±139.0, <i>t</i>=2.582,<i>P</i>=0.010). ROC curves showed that HU values at different locations of the surgical level all had predictive value for cage subsidence (upper vertebra: AUC=0.702, <i>P</i><0.01; lower vertebra: AUC=0.667, <i>P</i><0.01; endplate of the upper vertebra: AUC=0.657, <i>P</i><0.01; endplate of the lower vertebra:AUC=0.610, <i>P</i><0.01). The optimal thresholds for predicting cage subsidence for the upper vertebral body, lower vertebral body, endplate of the upper vertebra, and endplate of the lower vertebra were 325.0, 247.1, 533.1, and 547.4, respectively. However, the differences in predictive value among HU values from different vertebral locations were not statistically significant(<i>P</i>>0.05). In the validation set, the sensitivity and specificity of the HU value of upper vertebra for predicting cage subsidence were 6/7 and 9/10, respectively; for the lower vertebra, they were 5/7 and 9/10; for the endplate of the upper vertebra, they were 6/7 and 8/10; for the endplate of the lower vertebra, they were 5/7 and 8/10. <b>Conclusion:</b> The BMD of different parts of the vertebral body has potential predictive value for cage subsidence after ACDF surgery.